There have been known apparatus and methods for implementing multiple-orifice drop-on-demand ink jet print heads. In general, each channel of a multiple-orifice drop-on-demand ink jet operates by displacement of ink in an ink pressure chamber and subsequent emission of ink droplets from the ink pressure chamber through a nozzle. Ink is supplied from a common ink supply manifold through an ink inlet to the ink pressure chamber. A driver mechanism is used to displace the ink in the ink pressure chamber. The driver mechanism typically includes a transducer (e.g., a piezoceramic material) bonded to a thin diaphragm. When a voltage is applied to a transducer, the transducer displaces ink in the ink pressure chamber, causing ink flow through the inlet from the ink manifold to the ink pressure chamber and through an outlet and passageway to a nozzle. It is desirable to employ a geometry that permits multiple nozzles to be positioned in a densely packed array. The arrangement of the manifolds, inlets, and chambers and the coupling of the chambers to associated nozzles are not straightforward tasks, especially when compact ink jet array print heads are sought. Incorrect design choices, even in minor features, can cause nonuniform jetting performance.
Uniform jetting performance is generally accomplished by making the various features of each array channel in the ink jet print head substantially identical. Uniform jetting also depends on each channel being clear of air and internally generated gas bubbles which can form in the print head and interfere with jetting performance by blocking ink flow within the head. Therefore, the various features of the multiple-orifice print head must also be designed for effective purging.
An exemplary prior art ink jet print head construction is described in U.S. Pat. No. 4,680,595 of Cruz-Uribe, et al. FIGS. 1 and 4 of Cruz-Uribe et al. show two parallel rows of generally rectangular ink pressure chambers positioned with their centers aligned. The ink jet nozzles are coupled to different respective ink pressure chambers. The central axis of each nozzle extends normal to the plane containing the ink pressure chambers and intersects an extension portion of the ink pressure chamber. An ink manifold of substantially uniform cross-sectional area supplies ink to each of the chambers through a restrictive orifice that is carefully formed to match the nozzle orifice. Restrictive orifices are a form of ink inlet feature that acts to minimize acoustic cross-talk between adjacent channels of the multiple-orifice array. However, such restrictions often trap bubbles and, as a consequence, require frequent purging.
Effective purging depends on a relatively rapid ink flow rate through the various features of the head to sweep away bubbles. Ink flow rate at various locations in the manifold depends on the number of downstream orifice channels being purged and the cross-sectional area of the manifold. The flow rate is, therefore, greater at the upstream end of the manifold than at the downstream end where only a single orifice channel is drawing ink. The ink flow rate at the downstream end of the manifolds may not be sufficient to sweep away bubbles trapped in the manifolds.
U.S. Pat. No. 4,730,197 of Raman et al., which issued on a continuation application of the Cruz-Uribe et al. patent, describes additional embodiments thereof in FIGS. 11A and 11B including the same restrictor and ink manifold features.
U.S. Pat. Nos. 4,216,477 ("Matsuda et al. '477 patent") and 4,528,575 of Matsuda, et al. describe ink jet constructions in which ink is ejected parallel, instead of perpendicular, to the plane of the ink pressure chambers. In general, prior art array ink jet print heads in which the nozzle axes are parallel to the plane of the transducers are of relatively complex design and, therefore, difficult to manufacture. Each orifice channel has a rectangular transducer coupled to an ink chamber that communicates through a passageway to a nozzle orifice. In at least some embodiments described in these patents, the passageways are of different lengths, depending upon the location of the transducer relative to its associated nozzle.
Both patents show ink supply manifolds that have essentially constant cross-sectional areas over their entire lengths. FIG. 1 of the Matsuda et al. '477 patent shows a print head oriented vertically having an ink manifold with an ink supply opening at the bottom. The top of the manifold extends beyond the uppermost inlet to the uppermost orifice channel forming an upper cavity in which bubbles, being less dense than ink, can be entrapped. During purging, little or no ink flows through the upper cavity, effectively preventing the purging of bubbles. Over time, additional entrapped bubbles can coalesce into a single large bubble that effectively blocks ink flow to an upper orifice channel. Moreover, entrapped bubbles have a resonant frequency and cause pressure pulses generated in a pressure chamber to be non-uniformly reflected back to inlets of adjacent pressure chambers. Entrapped bubbles also dissipate energy at certain frequencies. Therefore, entrapped bubbles contribute to nonuniform jetting.
U.S. Pat. No. 4,387,383 of Sayko describes a multiple-orifice ink jet head. In FIG. 2, Sayko illustrates an ink manifold having a uniform cross-sectional area and in which the ink supply inlet is positioned at the top. Such a design minimizes entrapment of bubbles and facilitates their purgability, but exacerbates the entrapment of contaminants that are more dense than the ink. The lack of sufficient ink flow rate at the bottom end of such a manifold prevents contaminants from being swept away during purging and leads to clogging of features in the lowermost orifice channels.
U.S. Pat. No. 4,521,788 of Kimura et al. describes a multiple-orifice ink jet print head of radial construction with channel-to-channel feature uniformity that leads to uniform jetting performance. The radial ink supply manifolds of Kimura et al. illustrated in FIGS. 3, 6, and 7 are all of uniform cross-sectional area and include previously described features that can entrap contaminants or bubbles.
U.S. Pat. No. 4,367,480 of Kotoh describes a multiple-orifice ink jet print head having uniform feature sizes in each orifice channel. FIG. 4 of Kotoh illustrates an ink manifold having a nonuniform cross-sectional area. However, the shape illustrated can entrap contaminants or bubbles. FIGS. 8 and 10 of Kotoh illustrate a nonuniform serpentine ink inlet configuration that provides uniform acoustic performance among orifice channels. Also shown is an ink supply manifold with ink inlets at both ends. Such a configuration allows cross-flow purging (rapid ink flow in one ink inlet, through the manifold, and out the other inlet) that is effective at removing contaminants or bubbles from such an ink manifold, but not from the various features of each orifice channel. In addition, some compact head constructions do not have sufficient space for the additional manifold inlets required by cross-flow purging.
U.S. Pat. No. 5,087,930 of Roy et al. for DROP-ON-DEMAND INK JET PRINT HEAD, which is assigned to the assignee of the present application, describes a multiple-orifice print head of compact design. Pertinent components of the Roy et al. patent are diagrammed in FIGS. 1A, 1B, 2, 3, and 4 of the present application. FIGS. 1A and 1B are exploded views of the laminated plate construction of a print head 1 that includes a transducer receiving plate 2, a diaphragm plate 3, an ink pressure chamber plate 31, a separator plate 4, an ink inlet plate 5, a separator plate 6, an offset channel plate 7, an orifice separator plate 8, and an orifice plate 9. Plates 3 through 7 also form a set of black, yellow, magenta, and cyan ink manifolds. FIGS. 2-4 show each of the respective plates 5 through 7 in greater detail. In particular, a lower magenta ink manifold M is connected to the upper magenta ink manifold M' by an ink communication channel C. Ink is drawn as required from manifolds M and M' into multiple ink supply channels S, one for each magenta orifice channel of print head 1.
Referring now to FIGS. 3 and 4, it has been discovered that, during periods of no printing, a buoyant bubble B can become entrapped in an upper arch of ink communication channel C. During periods of printing, ink flows through channel C and manifold M' at a rate sufficient to drag bubble B to the inlet end of manifold M'. However, the rate of flow is insufficient to cause bubble B to be swept away through any of the ink supply channels S of print head 1. During purging, ink is caused to flow at an increased rate through manifolds M and M' and through ink supply channels S, causing bubble B to be drawn to a location B' at the right-hand end of manifold M'. However, bubble B' is not swept out of the rightmost end of manifold M' because only a single ink supply channel S' draws ink, resulting in a low ink flow rate. The buoyant force of bubble B' being greater than the ink flow rate-induced drag force on bubble B', causes bubble B' to remain entrapped. Moreover, entrapped bubble B' has a resonant frequency that acts to increase pressure pulse cross-talk among supply channels S within manifold M' whenever an ink orifice channel ejects ink drops at a rate near the resonant frequency of bubble B'. At some ejection rates, energy will be transferred to the bubble, causing it to grow, which can lead to starvation of print head 1.
To make matters worse, during normal printing the position of bubble B' in manifold M' depends on the droplet ejection patterns and rates for the multiple ink supply channels S coupled to manifold M'. The resulting cross-talk and bubble interaction induced jetting non-uniformities are visible in printed images as magenta intensity variations. Similar problems exist because of bubbles in the other manifolds of print head 1.
Although there are many prior art multiple-orifice ink jet print head designs, a need exists for an improved ink jet print head that is compact, has uniform jetting characteristics, and is capable of being completely purged of air or other gas bubbles.